초록 ▼

An engine exhaust gas purification system having a catalyst in an exhaust system of the engine, said catalyst reducing nitrogen oxide when exhaust gas generated by the engine is in an oxidizing state. In the system, engine operating parameters, including at least an engine speed and an engine load,

An engine exhaust gas purification system having a catalyst in an exhaust system of the engine, said catalyst reducing nitrogen oxide when exhaust gas generated by the engine is in an oxidizing state. In the system, engine operating parameters, including at least an engine speed and an engine load, are determined and catalyst temperature is determined, and air/fuel ratio is controlled in response to the detected parameters and the determined catalyst temperature, thereby enabling the catalyst to purify NOx in its optimum temperature characteristic range to achieve enhanced NOx constituent purification performance in an oxidizing environment. Alternatively, the air/fuel ratio is controlled in the stoichiometric or richer direction when the catalyst temperature is high, thereby protecting the catalyst from being damaged. The catalyst is a selective-reduction type nitrogen oxide reduction catalyst.

대표청구항 ▼

[ What is claimed is:] [1.] A system for purifying exhaust gas of an internal combustion engine having a catalyst in an exhaust system of the engine, said catalyst being a selective-reduction type nitrogen oxide reduction catalyst composed of a heat resistant inorganic oxide carrier and iridium born

[ What is claimed is:] [1.] A system for purifying exhaust gas of an internal combustion engine having a catalyst in an exhaust system of the engine, said catalyst being a selective-reduction type nitrogen oxide reduction catalyst composed of a heat resistant inorganic oxide carrier and iridium borne on the carrier as an active species and reducing nitrogen oxide when exhaust gas generated by the engine is in an oxidizing state, comprising:engine operating condition detection means for detecting parameters, including at least an engine speed and an engine load, indicative of operating conditions of the engine;catalyst temperature determining means for determining a temperature of the catalyst; andair/fuel ratio controlling means for controlling an air/fuel ratio, to be supplied to the engine in response to at least one of the detected parameters and the determined temperature of the catalyst, to a value in a lean direction when the determined temperature of the catalyst is within a predetermined range, and to a value in a rich direction, which is not more than a stoichiometric air/fuel ratio, when the determined temperature of the catalyst is outside of the predetermined range.